Much of the work on low VOC unsaturated polyester systems has focused on the use of waxes as a means of reducing emission. During polymer resin cure, waxes, which are initially dissolved or dispersed in the resin, form a thin film on the surface of the fabricated article. The film acts as a physical barrier preventing styrene (or monomer) from evaporating from the surface of the curing part. This reduces styrene emissions. Unfortunately, this waxy film substantially diminishes interlaminar adhesion, reducing the strength of molded articles made using a multilaminate construction.
An alternative to the use of wax, is to reduce the molecular weight of the unsaturated polyesters. The lower molecular weight polyester requires the use of less styrene (monomer) to maintain an appropriate working viscosity. This approach suffers from side reactions and reduced physical properties. It is desirable to maintain the physical properties of the system while using conventional resin systems containing monomers such as styrene, vinyl toluene, acrylates or diallylphthalate.
Benzopinacol has been known for some time as a suitable radical polymerization initiator. However, the reactivity and end product properties have not been enough to overcome the extra preparation expense compared to peroxide based radical initiators. To improve reactivity and solubility, the potassium/sodium salts of benzopinacol have been reacted with di-, tri-, and tetra chlorosilanes or polyorganosilane/siloxane materials. These products have had limited commercial success however they have never been shown to reduce VOC emissions.
Silyl ethers of benzopinacol for use as free-radical initiators are known. No evaluation of VOC emissions or catalyzed shelf-life were examined.
A polyurethane derivatized benzopinacol initiator is known and was reported to behave as a “living” catalyst. The shelf-life or VOC emission reduction of the resulting polymers was not reported. Monofunctional isocyanates, such as phenylisocyanate, have also been used to derivatize benzopinacol. These initiators were also found to be “living” catalysts.
Bromoacetyl derivatives of benzopinacol are known as flame retardant initiators for the polymerization of unsaturated polyester (UPE) systems. Additionally, phosphorus and silyl ethers of benzopinacol as flame retardant initiators for UPE systems have been reported.
The synthesis of spirocyclic esters of boric acid, including benzopinacol has been demonstrated. However, the use of these complexes in initiating the polymerization of unsaturated polyester (UPE) resins containing monomers and/or the reduced VOC emissions of resulting UPE resins and catalyzed shelf-life has not been examined.
The synthesis of chiral borate complexes including the use of benzopinacol as a ligand has been demonstrated. However, the use of these complexes in initiating the polymerization of unsaturated polyester (UPE) resins containing reactive monomers and/or the reduced VOC emissions of resulting UPE resins and catalyzed shelf-life has not been elucidated.